Sensation is produced when stimulation received from outside is converted to an electrical signal and transmitted to the brain through nerve cells. To convert external stimulation to an electrical signal, the existence of a receptor to perceive the external stimulation is essential.
TRPA1 is a non-selective cation channel belonging to a superfamily of transient receptor potential (TRP) ion channel and was found as a cold-temperature receptor (17° C.) in nociceptive neurons (Non Patent Document 1). After that, it is reported that TRPA1 is a chemoreceptor which responds to mustard oil, allyl isothiocyanate (AITC) contained therein, cinnamon, garlic, methyl salicylate, eugenol and the like, and is a pain receptor which responds to a cold temperature, mechanical and chemical stimulation (Non Patent Documents 2 and 3).
Further, it is recently reported that parabens and alkali agents respond to TRPA1 and substances which suppress irritation caused by parabens and alkali agents can be screened using transformed cells by TRPA1 gene (Patent Documents 1 and 2).
Thus, TRPA1 is a nociceptor of skin and mucous membrane and activated by various stimulation, and therefore inhibition of TRPA1 activity is considered to be effective to reduce the pain caused by various stimulation and so far agents for reduction of sensory irritation have been searched and evaluated by contacting a test agent and AITC with TRPA1-expressing cells and measuring the changes of intracellular calcium ion concentration induced by AITC through TRPA1 (Non Patent Document 4).